The EPP lightweight seat is formed by placing the steel frame in the mold cavity, so that the EPP is closely bonded to it. The difference of thermal expansion coefficient of different materials will cause the uneven distribution of residual stress, which will affect the final accuracy and performance of the workpiece. The deformation of the embedded steel wire frame after EPP molding was studied by changing several parameters such as forming state and prepressing time. The results show that the steel wire frame size control effect is best when the setting fixture is positioned in the hot state, the setting time is 1 hour, the negative tolerance of the lower support surface of the positioning fixture is 10 mm. It can be seen that the new process has the potential to reduce the overall weight of 5-15 kg in the seat, and reduce the number of parts and improve the assembly efficiency. The weight loss of the vehicle is also positively contributed, thus improving the range and reducing energy consumption. By changing the tooling temperature and preloading time, the warping deformation of the product is controlled, the tolerance range is reduced, and the loading demand of the seat is not affected. But now the research on the key technology of PMH process is mostly qualitative analysis, the durability of materials, the decomposition of materials after the life cycle and other issues need more in-depth study.